The present invention relates generally to fuel injection systems for internal combustion engines, and more-specifically to techniques for estimating fuel injection quantities in such systems.
In recent years, advances in fuel systems for internal combustion engines, and particularly for diesel engines, have increased dramatically. However, in order to achieve optimal engine performance at all operating conditions with respect to fuel economy, exhaust emissions, noise, transient response, and the like, further advances are necessary. As one example, operational accuracy with electronically controlled fuel systems can be improved by reducing variations in injected fuel quantities.
A number of techniques are known for reducing injected fuel quantity variations such as, for example, robust system design, precision manufacturing, precise component matching, and electronic control strategies. However, conventional manufacturing approaches for improving performance, such as tightening tolerances and the like, are typically cost prohibitive, and conventional control approaches such as open-loop look-up tables have become increasingly complex and difficult to implement as the number of degrees of freedom to control have increased, particularly with multiple-input, multiple-output (MIMO) control systems. In fact, both of these approaches improve accuracy only during engine operation immediately after calibration in a controlled environment, and neither compensate for deterioration or environmental noise changes which affect subsequent performance. Closed-loop control systems for controlling injected fuel quantity variations are accordingly preferable, but typically require additional sensors to measure appropriate control parameters.
One known technique for implementing such a closed-loop control system without implementing additional sensors is to leverage existing information to estimate injected fuel quantity; i.e., implementation of a so-called xe2x80x9cvirtual sensor.xe2x80x9d One example of a known control system 10 including such a virtual sensor is illustrated in FIG. 3. Referring to FIG. 3, system 10 includes a two-dimensional look-up table 14 receiving an engine speed/position signal via signal line 12 and a desired fuel injection quantity value from process block 16 via signal path 18. Table 14 is responsive to the engine speed/position signal and the desired fuel injection quantity value to produce an initial fueling command as is known in the art. The virtual injected fuel quantity sensor in system 10 typically comprises a two-dimensional look-up table 20 receiving the engine speed/position signal via signal path 12 and a fuel pressure signal from signal path 22. Table 20 is responsive to the fuel pressure and engine speed/position signals to produce an injected fuel quantity estimate that is applied to summing node 24. Node 24 produces an error value as a difference between the desired fuel injection quantity and the injected fuel quantity estimate and applies this error value to a controller 26. Controller 26 is responsive to the error value to determine a fuel command adjustment value, wherein the initial fueling command and the fuel command adjustment value are applied to a second summing node 28. The output of summing node 28 is the output 30 of system 10 and represents a final fueling command that is the initial fueling command produced by table 14 adjusted by the fuel command adjustment value produced by controller 26.
While system 10 of FIG. 3 provides for a closed-loop fuel control system utilizing a virtual sensor to achieve at least some control over variations in injected fuel quantities, it has a number of drawbacks associated therewith. For example, a primary drawback is that prior art systems of the type illustrated in FIG. 3 are operable to compensate for variations in only a single operating parameter. Control over variations in additional parameters would require prohibitively large and difficult to manage multi-dimensional look-up tables, wherein such tables would be limited to only operating parameters capable of compensation via look-up table techniques. For operating parameters that deteriorate or change with time, for example, compensation via look-up tables simply does not work without some type of scheme for updating such tables to reflect changes in those operating parameters.
As another drawback of prior art systems of the type illustrated in FIG. 3, such systems are not closed-loop with respect to injector-to-injector fueling variations. For example, referring to FIG. 16, a plot 35 of measured fuel injection quantity vs. injector actuator commanded on-time (i.e., desired fueling command) for each injector (cylinder) of a six-cylinder engine, is shown wherein the between-cylinder fueling variations are the result of various mismatches in the fueling system hardware. As is apparent from plot 35, the between-cylinder fuel injection quantity variations are quite pronounced and generally unacceptable in terms of accurate fueling control. While known cylinder balancing techniques could reduce such cylinder-to-cylinder fueling variations, the fuel control system of FIG. 3 would be ineffective in reducing such variations. Moreover, the fuel control system of FIG. 3 would further be ineffective in reducing engine-to-engine fueling variations. Referring to FIG. 17, for example, plots of average injected fuel vs. injector on-time for three engine fueling extremes are illustrated. Nominal engine fueling requirements are illustrated by curve 36, minimum engine fueling conditions are illustrated by curve 38 and maximum engine fueling conditions are illustrated by curve 40. While engines of the same type may be designed for identical fueling requirements, their actual fueling requirements may fall anywhere between curves 38 and 40. Unfortunately, the prior art fuel control system of FIG. 3 cannot compensate for such engine-to-engine fueling variations. In general, if such control parameter variations are not attributable to the operating parameter for which the system is designed to compensate for, but are instead attributable to other error sources for which the control system of FIG. 3 is not designed to compensate for, the system performance may actually be worse than would otherwise be the case with conventional fuel control techniques.
By the nature of their uses in a wide variety of applications, engines are typically required over their operating lifetimes to work in environments wherein many internal and external parameters that affect engine performance may vary, cannot be controlled and/or cannot be, or typically are not, measured. Heretofore, known control systems have attempted to improve injected fueling accuracy using a parameter that is both measurable and controllable. Such systems typically operate by making control changes, based on an estimated sensitivity in the fueling quantity, to this measurable and controllable parameter using assumed values for other internal and/or external parameters rather than taking into account performance effects and interactions of these other parameters. By contrast, if the injected fueling quantity can be estimated utilizing a sensor or virtual sensor that is independent of many of the internal and external parameters that affect the engine""s injected fueling quantity, a robust closed-loop fueling quantity control can be performed directly on the estimated fuel quantity rather than on only one of the control parameters that affect the fueling quantity. What is therefore needed is an improved strategy for adaptively estimating injected fuel quantities based on real-time performance of certain fuel system operating conditions throughout an injection event to thereby allow for robust and accurate operation as well as straightforward integration into complex fuel control systems. Ideally, such a strategy should be capable of minimizing between-cylinder and between-engine fueling variations.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a fuel control system for an internal combustion engine comprises means for storing pressurized fuel, means for injecting a quantity of fuel from the means for storing pressurized fuel into a combustion chamber of an internal combustion engine, means for determining a first energy level associated with the means for storing pressurized fuel prior to injection of the quantity of fuel and a second energy level associated with the means for storing pressurized fuel after injection of the quantity of fuel, and means for determining an estimate of the quantity of fuel as a function of a difference between the first and second energy levels.
In accordance with another aspect of the present invention, a fuel control system for an internal combustion engine comprises a collection unit for receiving pressurized fuel, a fuel injector responsive to a fueling command to dispense a quantity of fuel into a combustion chamber of an internal combustion engine, a pressure sensor operable to sense pressure of the pressurized fuel within the collection unit and produce a pressure signal corresponding thereto, and a control computer responsive to the pressure signal to determine a change in fuel pressure value as a function of the pressure signal prior to injection of the quantity of fuel and of the pressure signal after injection of the quantity of fuel. The control computer is operable to determine an estimate of the quantity of fuel as a function of the change in the fuel pressure value.
In accordance with yet another aspect of the present invention, a fuel control system for an internal combustion engine comprises a collection unit for receiving pressurized fuel, a fuel injector responsive to a fueling command to dispense a quantity of the pressurized fuel during an injection event, means for sensing pressure of the pressurized fuel and producing a pressure signal corresponding thereto, and a control circuit responsive to the pressure signal to determine a discharged fuel estimate as a function of a fuel pressure change across the injection event. The control circuit is also responsive to the pressure signal to determine a control flow estimate as a function of an injection pressure during said injection event, and to determine an estimate of the quantity of fuel as a function of the discharged fuel estimate and the control flow estimate.
In accordance with still another aspect of the present invention, a method of controlling a fuel system of an internal combustion engine comprises the steps of providing a supply of pressurized fuel, dispensing a quantity of the pressurized fuel pursuant to an injection event, determining a change in pressure of the supply of pressurized fuel across the injection event, and determining an estimate of the quantity of the pressurized fuel as a function of the change in pressure of the supply of pressurized fuel.
In accordance with a further aspect of the present invention, a fuel control system for an internal combustion engine comprises a collection unit for receiving pressurized fuel, a number of fuel injectors each responsive to a separate fueling command to dispense a quantity of the pressurized fuel into one of a corresponding number of combustion chambers of an internal combustion engine, a pressure sensor operable to sense pressure of the pressurized fuel within the collection unit and produce a pressure signal corresponding thereto, an engine speed sensor operable to sense engine speed and produce an engine speed signal corresponding thereto, and means for determining a pressure error for each of the number of combustion chambers as a function of a desired fuel injection pressure and the pressure signal while dispensing the quantity of the pressurized fuel therein, means for measuring the quantity of the pressurized fuel dispensed in each of the number of combustion chambers and producing a corresponding number of measured fuel quantity values, means for determining a fuel quantity error for each of the number of combustion chambers as a function of a corresponding one of the measured fuel quantity values and an associated desired fuel quantity value, means for determining a speed error for each of the number of combustion chambers as a function of the engine speed signal over one engine cycle and the engine speed signal over one firing cycle associated with a corresponding one of the combustion chambers, and means for comparing the pressure errors, the fuel quantity errors and the speed errors for predefined combustion chamber combinations with a fault tree matrix and logging fault codes indicated thereby within a memory unit. In accordance with still a further aspect of the present invention, a method of controlling a fuel system, comprising the steps of providing a supply of pressurized fuel, dispensing a quantity of the pressurized fuel within each of a number of combustion chambers of an internal combustion engine pursuant to an associated injection event, determining a pressure error for each of the number of combustion chambers as a function of a pressure of the pressurized fuel during the associated injection event and a desired fuel pressure value corresponding thereto, measuring the quantity of pressurized fuel dispensed within each of the combustion chambers and producing a corresponding number of measured fuel quantity values, determining a fuel quantity error for each of the number of combustion chambers as a function of a corresponding one of the number of measured fuel quantity values and an associated desired fuel quantity value, determining an engine speed error for each of the number of combustion chambers as a function of engine speed over at least one engine cycle and engine speed over a firing cycle associated with a corresponding combustion chamber, and comparing the pressure, fuel quantity and engine speed errors for predefined combinations of combustion cylinders with a fault tree matrix and logging faults indicated thereby within a memory unit.
In accordance with yet another aspect of the present invention, a method of determining bulk modulus information of pressurized fuel in a fuel system of an internal combustion engine comprising the steps of providing a supply of pressurized fuel, determining a rate of change of pressure associated with the supply of pressurized fuel over a fuel pressure range, and producing an instantaneous bulk modulus value of the pressurized fuel as a function of the rate of change of pressure.
In accordance with yet a further aspect of the present invention, a method of determining bulk modulus information of pressurized fuel in a fuel system of an internal combustion engine comprises the steps of providing a supply of pressurized fuel, determining a slope of a rate of change of fuel pressure associated with the supply of pressurized fuel, determining an intercept value of the rate of change of fuel pressure at a predefined pressure value, producing a bulk modulus slope value as a function of the slope of the rate of change of pressure, and producing a bulk modulus intercept value as a function of the intercept value.
One object of the present invention is to provide an improved fuel control system utilizing adaptive closed-loop feedback techniques for accurately estimating injected fuel quantities without adding further sensors.
Another object of the present invention is to provide such a system wherein injected fuel quantities are estimated as a function of a change in energy of a fuel collection unit operable to supply pressurized fuel to a number of fuel injectors.
Yet another object of the present invention is to provide such a system wherein the change in energy of the fuel collection unit is determined as a change in pressures of the fuel collection unit at least prior to and after an injection event.
Still another object of the present invention is to provide such a system including provisions for estimating a bulk modulus of the fuel within the collection unit and adjusting the injected fuel quantity estimates in accordance therewith.
A further object of the present invention is to provide such a system wherein the fuel quantity estimates are adjusted in accordance with corresponding estimates of one or more control flow events.
Still a further object of the present invention is to provide such a system wherein the fuel quantity estimates are adjusted in accordance with corresponding estimates of parasitic leakage estimates.
Yet a further object of the present invention is to provide a fuel control system operable to measure or estimate injected fuel quantities wherein error values between desired fuel and measured or estimated injected fuel, between desired fuel pressure and measured fuel pressure during injection, and between average engine speed over an engine cycle and engine speed over an injection event are generated and compared with a fault tree matrix to determine and log appropriate fuel system failures.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.